Vehicles may be fitted with evaporative emission control systems such as onboard refueling vapor recovery (ORVR) systems. Such systems capture and reduce release of vaporized hydrocarbons to the atmosphere, for example fuel vapors released from a vehicle gasoline tank during refueling. Specifically, the vaporized hydrocarbons (HCs) are stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel.
Various approaches have been developed for detecting fuel vapor leaks in such ORVR systems. However, the inventors have recognized several potential issues with such methods. The inventors have recognized that it is possible for a reverse flow of air and/or fuel vapors through the ORVR system (for example, from the intake manifold to the fuel tank) to occur. Specifically, such reverse flows may occur in the case where a canister check valve is stuck open and/or a canister purge valve is stuck open. Likewise, it is also possible for the canister purge valve and/or check valve to degrade in boosted engines wherein the intake manifold pressure (MAP) is substantially above atmospheric pressure levels. Consequently, the purge flow may overcome a pressure relief valve (such as a pressure relief valve in the fuel tank cap), causing the fuel tank and the fuel vapor canister to over-inflate and exceed design limits of pressure. Furthermore, the reverse flow of fuel vapors through the canister purge system may cause hydrocarbon vapors to escape into the atmosphere and degrade emissions quality.
Thus, in one example, some of the above issues may be addressed by a method of monitoring reverse flow of fuel vapors and/or air through a vehicle fuel vapor recovery system, said fuel vapor recovery system coupled to an engine intake of a boosted internal combustion engine. In one example, the method comprises, intermittently adjusting a restriction in the fuel vapor recovery system during boosted conditions, and indicating degradation based on one or more of a change in a pressure value, or based on a change in flow in the fuel vapor recovery system.
In this way, by sensing changes in fluid pressure and/or fluid flow in a fuel vapor recovery system, for example fluid pressure and/or fluid flow changes across a component of the fuel vapor recovery system (such as a fuel tank pressure sensor), improper flow through a fuel vapor recovery system coupled to a boosted engine system may be identified. By identifying improper flow of air through the fuel vapor recovery system, for example, reverse flow of boosted air from an engine intake manifold, degradation of the fuel vapor recovery system may be reduced. By promptly disabling boost responsive to the reverse flow, damage to fuel vapor system components, such as valves, canisters, and/or fuel tanks, may be reduced. Additionally, reverse flow induced excessive evaporative emissions may also be addressed.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.